Proper localization of anatomical landmarks is necessary for performing planned surgical procedures in the lumbar spine accurately, including confirmation of the proper vertebral levels to operate. This is typically achieved through the use and interpretation of intraoperative radiography by the surgeon. This is necessary because, in many situations, the exact locations of anatomical structure the surgeon desires to approach are not externally apparent by direct inspection of the patient's visible body surface when positioned for the operation. In such situations, radiographic images obtained with appropriate radio-opaque markers in place provide the surgeon with confirmation of the relationships of these markers to the underlying anatomical structures the surgeon desires to approach. In operations which do not involve the implantation of instrumentation hardware, one or two plain x-rays are usually sufficient to produce enough information to accurately and confidently achieve the surgical goals.
However, operations involving the placement of hardware instrumentation (e.g. pedicle screws) for lumbar spinal fusion operations, which have many steps, typically require multiple radiographic images to be performed during the operation. These radiographic images require time to perform and develop. Further, each radiograph exposes the patient to radiation, which has medical risks. This is particularly problematic in percutaneous and minimally invasive techniques for instrumentation, which are used to minimize the disruption of normal anatomical structures caused by traditional surgical exposures. The resulting limitations on visualization achievable in these procedures make reliance on radiographic guidance all the more crucial.
Customarily, intraoperative fluoroscopy is used to accommodate the much more frequent radiographic images that must be obtained and interpreted during these procedures. Fluoroscopy, however, exposes the patient as well as care providers, including the surgeon and surgical team, to much higher doses of radiation than they would otherwise receive from plain radiographs. Over a provider's career, such cumulative radiation exposure can greatly increase the risk of development of iatrogenic malignancies. Techniques to minimize the radiation exposure to the surgical team which are currently employed include radiographic shielding, as well as stereotactic guidance-based techniques which rely on registration of intraoperative radiographic anatomy, acquired fluoroscopically, with previously acquired patient images. Such techniques, however, can expose the patient to as much intraoperative radiation as a CT scan, which represents a substantial dose and would not be required were the intraoperative registration not necessary.